There are already known various constructions of fuel cells, among them such in which it is necessary or advantageous to treat selected regions of various fuel cell components with flowable substances. For example, it may be desired to wetproof such selected regions by applying thereto an initially flowable substance, such as a fluorocarbon dispersion, that solidifies after its application and thereafter confers the desired wetproof characteristic on such regions. The presence of such fluorocarbon or similar deposits on or in fuel cell electrodes is often necessary to create corrosion resistant areas within the cell.
The need for or desirability of providing such wetproofed or similarly treated regions has already been previously recognized, as has the need for giving such treated regions quite sharply defined outlines or contours. Particularly in order to satisfy the last-mentioned need, one method that is currently in widespread use for applying such wetproofing or similar compounds is the so-called screen printing process technique, which involves the application of the respective flowable substance, such as a dispersion or "ink", to the selected region or regions of a substrate through a screen while the remaining regions of the substrate are masked. By properly choosing the consistency or viscosity of the substance, the length of the time interval during which the screen/mask member is in contact with the substrate, the amount and distribution of the substance present on the screen/mask member at the beginning of such time interval, and the manner in which the substance is forced, such as by a squeegee or the like, through the screen, it is possible to control, within limits, not only the degree of conformity of the contour of the thus treated region to the desired one, but also, when the substrate is porous, the depth of penetration of the substance into the substrate at the affected region.
However, experience has shown that, while the screen printing process is ideally suited for applying thin coats of dispersions on the surfaces of smooth surfaced substrates, it in many instances leaves much to be desired when it is attempted to use it for applying coatings to rough or porous substrate. Moreover, this process is not capable of easily and reliably forcing a semi-liquid substance into the structure of a porous material, particularly when it is desired to cause the substance to permeate into more than just the area immediately underlying the surface to which the substance is applied and especially when the substance is to impregnate the selected region of the substrate throughout the thickness of the latter. Yet, such impregnation has been accomplished in the past with some degree of success by screen printing the part while it was held under partial vacuum that is applied in such a manner as to draw the substance deeper into the substrate. Nevertheless, even this process is less than satisfactory in many cases, especially because the constraints placed on the selection of the viscosity of the substance by use of the screen printing process, in combination with the vagaries of the vacuum drawing process, result in less than ideal impregnation of the affected region of the substrate by the substance and/or in less than accurate definition of the boundary of the affected region or conformity to its desired course. More particularly, given the nature of variations in substrate pore spectra and the vagaries of screen process printing, dimensional control of the fluorocarbon deposit is difficult to achieve. In addition, the necessity for a screen process fluorocarbon ink which will penetrate the porous substrate, particularly an electrode, and yet not run through the screen between printing cycles makes the process difficult to manage. Based on the above considerations, it has been determined that the screen printing process is not suited to high production subsurface wetproof application.
Accordingly, it is a general object of the present invention to avoid the disadvantages of the prior art.
More particularly, it is an object of the present invention to provide a method of impregnating selected regions of porous substrates, especially of fuel cell electrode plates, with flowable substances capable of subsequent solidification, which method does not possess the disadvantages of the known methods of this kind.
Still another object of the present invention is to develop the impregnating method of the type here under consideration in such a manner as to assure penetration of the substance into and substantially uniform distribution of such substance throughout the affected region of the porous substrate.
A further object of the present invention is to present a method of the above kind the performance of which will result in much better coincidence than before of the actual boundaries of the impregnated region with the desired ones.
It is yet another object of the present invention to devise an apparatus that is well suited for the performance of the method of the above type.
A concomitant object of the present invention is design the apparatus of the above type in such a manner as to be relatively simple in construction, inexpensive to manufacture, easy to use, and yet reliable in operation.